The present invention relates to the preparation of tea products and more particularly to water soluble tea extracts prepared by acid hydrolysis of the spent tea residues formed during the hot aqueous extraction of tea leaves in the production of water soluble tea extracts.
The products of tea have been increasingly marketed in the form of water-soluble tea extracts, usually in the form of dry powders. Substantial research activity has been directed to improve the quality of tea beverage, having a flavour and colour as close as possible to that obtained by brewing tea leaves. Another aspect of soluble tea manufacturing is to increase the yield of tea soluble solids.
Methods of obtaining tea extracts from tea leaves using a series of countercurrent stages or a two-stage extraction are well-known. Temperatures of aqueous extraction vary from room temperature to elevated temperatures as high as 180.degree. C. with elevated pressures.
However, the predominantly remaining spent tea, i.e., tea extraction residue material, is currently discarded.
In U.S. Pat. No. 4,668,525, a method is described for treating the spent tea leaf from a tea extraction process which comprises acidifying the spent tea leaf to reduce the pH to within the range of about 2.0 to 3.0 and subjecting the acidified spent tea leaf to further extraction with aqueous solvent at pressures of about 80-100 psig and temperatures of about 140-170.degree. C. for at least 4 minutes and separating the remaining tea leaf solids from the aqueous solvent to leave a high temperature/high pressure aqueous extract. However, the resulting extract was found to have an unacceptable bitter taste with a pruny off-flavour.
Methods have been described for treating raw tea ingredients by means of enzymes in order to obtain water soluble tea extracts. For instance, Japanese Patent No. 71017958 describes the extraction of tea with a protopectinase and cellulase, Japanese Patent No. 82047465 describes the production of cereal teas which comprises heating at 110-220.degree. C., impregnating with an aqueous solution of amylase, protease or cellulase, heat-drying at 50-100.degree. C. and roasting at 100-170.degree. C., and Japanese Patent No. 84034849describes the production of instant tea by extraction with a mixture of glutinous starch, alpha amylase and at least one enzyme selected from beta amylase, cellulase and protease. EUR-A-135222 describes a process of treating black tea before extraction with a solution of tannase and one or more cell wall digesting enzymes such as cellulase.
Russian Patent No. 683709 describes the treatment of tea waste by fermenting with a mixture of pectolytic and cellulolytic enzymes and afterwards adding amino acids and saccharose and extracting at 70.degree. to 90.degree. C.